One of the things that I've done for iOS developers is provide something called "WebCycript": a reasonably seamless way for you to just <script language="text/cycript"> in an HTML document being rendered (in this case, on the lock screen, to allow for easy-to-make lock screen widgets), and then have access to Objective-C APIs (even using Objective-C syntax; cycript.org for some example code; and I now wish I had finished putting up the new fancier website I was working on a few weeks ago ;P). If I supported something like this on desktop systems (along with the other arguably-simpler things, such as the embeddable browser), would that be valuable help for this problem space?